Sialyltransferase has been found to be elevated in the sera of breast cancer patients. Specific cancer associated isoenzymes may be present which could be used as markers for breast cancer. Our initial studies using preparative flat bed isoelectric focusing did not indicate any novel isoenzymes of sialyltransferase in sera from breast cancer patients. Preliminary results have indicated two major serum sialytransferase enzymes with PI's of 4.9 and 5.3 in normals and cancer patients. However, in those studies a significant amount of enzyme activity was not recovered from the plates. Therefore, several new techniques will be attempted to increase recovery of enzyme activity while still maintaining good separation and fine resolution. These proposed studies include use of photoaffinity labeled substrates and new techniques in column isoelectric focusing. These analyses should provide definitive information on the usefullness of serum sialyltransferase isoenzyme assays in breast cancer. Other studies will be performed which will assess the serum sialyltransferase inhibitory activity of several nucleoside-sugar antibiotics. The chemotherapeutic potential of these compounds and other N6-substituted adenosine analogs will also be evaluated in rodents with several transplantable mammary tumors. These studies should lead to the development of better therapeutic strategies in the diagnosis and treatment of breast cancer.